High-availability computer systems, such as telecommunications networking computers and internet servers, require several backup power supplies, such that, if one power supply fails, operations of the computer systems would not be interrupted. Further, it would be undesirable to take the computer systems off-line in order to replace a malfunctioned power supply. Therefore, high-availability systems are generally designed to receive hot-plug power supplies. A hot-plug power supply is a power supply that can be hot-inserted. That is, a malfunctioned hot-plug power supply may be replaced, or a new hot-plug power supply may be connected to the system, while the system is operating. Ideally, operations of the high-availability system are not interrupted when hot-plug power supplies are replaced or added.
In reality, however, the risk of disrupting operating power during hot-insertion is high. Generally, prior art power supplies and high-availability computer systems have comparable capacitance. One such system is illustrated in FIG. 1. As an example, prior art power supply 102 has an output capacitor having a capacitance of 5C which is uncharged before power supply 102 is installed. As shown, computer system 104 also has a capacitance of 5C. Thus, when the prior art hot-plug power supply 102 is hot-inserted into the computer system 104, a glitch will be produced as currents are drawn from the computer system 104 to the uncharged output capacitors of the power supply 102. For high-speed computers such as internet servers, a tiny glitch caused by the slightest disruption in the supply power may lead to failure in the logic circuits or result in a crash. In some instances, valuable electronic components may be damaged and data may be irrecoverably lost. Therefore, the prior art power supply is unsuitable for hot-insertion.
Numerous solutions, however, have been devised to prevent the occurrence of these glitches such that prior art power supplies may be used for hot-insertion. One prior art method was to install on the high-availability systems certain mechanical features, such as special handles, special connectors or thumb screws, which prolong the power supply insertion time and allow the output capacitors of the power supplies to be charged slowly. This method, however, is not completely effective because a service person may inadvertently insert a new power supply faster than it is anticipated. In those situations, a large glitch may be produced. As a result, the computer system may experience power interruption.
Another prior art solution was to connect diodes between outputs of prior art power supplies and the computer systems. As diodes do not allow current to pass in the reverse direction, uncharged power supplies would not draw currents from the systems when hot-inserted. This solution, however, is only efficient in low current applications. In high current applications, such as high-availability computers, power dissipation across the diodes would be enormous.
Therefore, what is needed is an improved hot-plug power supply for high-availability systems which significantly reduces the size of glitches caused by hot-insertion. What is also needed is a hot-plug power supply having a low power dissipation level in high current applications. What is further needed is a hot-plug power supply having an ultra-fast dynamic response time such that the system may recover from glitches expediently. What is also needed is a hot-plug power supply that includes an indicator for signaling the computer system and a service person that the power-supply is successfully installed.